load sensing technologies - robert bosch gmbh€¦ · load sensing technologies. dcsn/slm-dk |...
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Load sensing technologies
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Load sensing technologies
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What is load sensing?“Sensing the load pressure downstream of an orifice and…
“Lastunabhängige Durchflussverteilung”
…adjusting the pump flow rate to maintain a constant pressure drop across the orifice…
…meaning a constant flow is achieved regardless of a change in load pressure”
Non-compensated and compensated valves‒ Load dependent and load independent with multiple functions
Types of compensation‒ Pre compensated (Load sensing) & Post compensated (Flow-sharing / LUDV)
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Load sensing technologies
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What is load sensing?Open Center LS Closed Center LS
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Load sensing technologies
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What is load sensing?Open Center LS Closed Center LS
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Load sensing technologies
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Flow Equation
A
QV
∆p
QV = α x A x ∆ p2ρ
α x = K2ρ
QV = K x A ∆ p
QV = f (A, ∆ p) ∆ p = const. QV = f (A)
QV = FlowA = Opening area of orifice∆ p = Differential pressureα = Flow coefficientρ = Oil- Density
Load- dependent System (Open Center Control)
Load- independent System(Load Sensing Control)
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Load sensing technologies
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Under-saturation condition∆p
qpump
Avalve
[mm
²][l/
min
][b
ar]
∆p
qpump
qrequired [l/min]
Avalve50 l/min
18,5 mm²
20 bar
100 l/min
36,9 mm²
20 bar
100 l/min
55,3 mm²
8,9 bar
73,8 mm²
100 l/min
5 bar
20 bar
Max 100 l/min
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Load sensing technologies
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Pre- and post-compensation – basic circuits
Load sensing pump
Pressure compensator(normally open)
Metering element(main spool)
Actuator(cylinder or motor)
Load signal check
Biasspring
Load signal check
Metering element(main spool)
Pressure compensator(normally closed)
Load sensing pump
Actuator(cylinder or motor)
No bias spring
Pre-compensated Post-compensated
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Load sensing technologies
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Pre-compensation - basic circuit
• Start of movement load-/flow-independent
• Fine control range load-independent but flow-dependent
• Independent movement during parallel operation
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Load sensing technologies
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Pre-compensation - saturated conditionLoad50 bar
Load250 bar
50 bar 250 bar
250 bar270 bar 270 bar
57 bar 257 barBias spring 7 bar
Bias spring 7 bar
FR = 20 bar
∆p 213 bar
∆p 7 bar
∆p 13 bar
∆p 7 bar
Max flow = 100 l/min
Required flow60 l/min
Required flow30 l/min
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Load sensing technologies
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Pre-compensation - under-saturated conditionLoad50 bar
Load250 bar
50 bar 250 bar
250 bar251,1 bar 251,1 bar
57 bar 251,1 barBias spring 7 bar
Bias spring 7 bar
FR = 20 bar
∆p 194,1 bar
∆p 7 bar
∆p “0” bar
∆p 1,1 bar
Max flow = 100 l/min
Required flow80 l/min
Required flow50 l/min
Actual flow80 l/min
Actual flow20 l/min
∆p =Qv2 � ρ
A2 � α2 � 2
A = Qv
α� 2ρ �∆p
50 l/min
7 bar
31,2 mm²
20 l/min
= 31,2mm²
= 1,1 bar
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Load sensing – pre-compensated circuit
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Consumer flows with reduced pump flow
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Load sensing – pre-compensated circuit
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LS pressure limitation • Function analogue to pressure cut-off• Limitation of the LS-signal, therefore
nearly free of losses• Local as well as global pressure
limitation is possible
Local LS pressure limiters
Global LS pressure limiter
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Load sensing – pre-compensated circuit
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LS unloading • LS unloading is realized through the main spool
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Load sensing – pre-compensated circuit
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Example: M4-12 High pressure load sensing control block
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Flow sharing (LUDV) – post compensated circuit
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Basic circuit
• Start of movement load-/flow-independent
• Fine control range load/flow-independent • Independent movement during parallel
operation
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Flow sharing (LUDV) – post compensated circuit
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Saturated condition
Load50 bar
Load250 bar
50 bar
270 bar
250 bar
∆p 20 bar
∆p 200 bar
Required flow60 l/min
Required flow30 l/min
270 bar
250 bar
250 bar
∆p 20 bar
∆p “0” bar
250 bar
FR = 20 bar
Max flow = 100 l/min
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Flow sharing (LUDV) – post compensated circuit
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Undersaturated condition
Load50 bar
Load250 bar
50 bar
261,8 bar
250 bar
∆p 11,8 bar
∆p 200 bar
Required flow80 l/min
Required flow50 l/min
261,8 bar
250 bar
250 bar
∆p 11,8 bar
∆p “0” bar
250 bar
FR = 20 bar
Max flow = 100 l/min
Actual flow61,5 l/min
Actual flow38,5 l/min
020406080
020406080
10005
1015202530
0 10 20 30 40 50 60 70 80 90 100
110
120
130
140
150
160
170
180
190
200
11,8 bar
130 l/min
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Flow sharing (LUDV) – post compensated circuit
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Flow sharing Consumer 1Qrequired = 80,0 l/minQactual = 61,5 l/minRatio = 1 : 0,77
Consumer 2Qrequired = 50,0 l/minQactual = 38,5 l/minRatio = 1 : 0,77
PumpQrequired = 130,0 l/minQmax = 100,0 l/minRatio = 1 : 0,77
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Flow sharing (LUDV) – post compensated circuit
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Consumer flows with reduced pump flow
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Flow sharing (LUDV) – post compensated circuit
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End stop condition
Ppump = PLS
No flow can pass through compensator
∆p = 0
300 bar
300 bar 300 bar
FR = 20 bar
DR = 300 bar
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Flow sharing (LUDV) – post compensated circuit
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LS pressure limitation
FR = 20 bar
DR = 300 bar LSRV = 280 bar
300 bar
280 bar280 bar
∆p 20 bar
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Flow sharing (LUDV) – post compensated circuit
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Port pressure limitation • Local port pressure limitation only possible via full flow shock valves
• High loss and heating• Only global LS pressure limitation is
possible
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Flow sharing (LUDV) – post compensated circuit
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LS unloading
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Post compensated circuit (LUDV)
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Example: M7-22 High pressure flow sharing control block
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Combination circuit
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LS and LUDV – checklist
1
2
3
1) Check valve from pre-compensated LS-signal to common LS-signal
2) LS copy valve (if necessary)
3) No valves in the LS line between pump and LUDV valve
4) Main relief valve (or PC)5) LS relief valve setting = pump
standby pressure below the MRV (or PC)
6) LS unloading valve
5
64
LS (pre compensated) LUDV (post compensated)
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Combination circuit
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LS and LUDV – system features• LS circuit will have priority over the
LUDV circuit in under-saturated condition
• LUDV circuit will share the remaining flow when the required LS functions are saturated
LS (pre compensated) LUDV (post compensated)
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Load sensing technologies
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Summary of featuresLS (pre-compensation) Good fine-control Start of movement load-independent Load-independent parallel operation of several
actuators under saturated condition Possibility for local LS pressure limitation
Load-dependent under under-saturated condition, i.e. system reacts like throttle control
Sensitive against oscillations, therefore intensive prototype commissioning may be necessary
LUDV (post-compensation) Good fine-control Start of movement load-independent Load-independent parallel operation of several
actuators also under under-saturated condition
No possibility for local LS pressure limitation Sensitive against oscillations, therefore intensive
prototype commissioning may be necessary
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Thanks for your attention